It may be that there is no such thing as a date of 31 October 2019 for a no-deal UK withdrawal from the EU. On 9 April 2019, according to Le Monde, Michel Barnier, chief negotiator for the European Council in the withdrawal negotiations with the UK, said: ‘The EU will never take a decision on a ‘no deal’. That will be a choice for the British.’

On 10 April, the European Council adopted a very obscure decision. ‘In response [to a British request], the European Council agrees to an extension to allow for the ratification of the Withdrawal Agreement. Such an extension should last only as long as necessary to allow for the ratification of the Withdrawal Agreement and, in any event, no longer than 31 October 2019. If the Withdrawal Agreement is ratified by both parties before this date, the withdrawal will take place on the first day of the following month.’ The European Council ‘also notes that…the United Kingdom has a right to revoke its notification at any time’.

‘Ratification of the withdrawal agreement’ was presumably supposed to mean acceptance within the UK of the then Prime Minister’s draft agreement; and ‘ratified by both parties’ was presumably intended to mean formal acceptance, rather than ratification in the technical sense of international treaty law.

The decision of the European Council does not say what would happen if the Withdrawal Agreement is not ratified by both parties before 31 October 2019. It does not use the formula of Article 50(3) to the effect that ‘the Treaties shall cease to apply to the State in question’ at the expiration of the time-limit.

Nevertheless, it seems to be taken for granted that the UK will cease to be an EU member state on October 31, 2019, if its notification of intention to withdraw is not revoked and the period of negotiation of a withdrawal agreement is not extended.

That view is correct only if the European Council’s decision of 10 April 2019 created a second time-limit for conclusion of an agreement and if such a decision would be legally valid, and if the decisions taken by the EU institutions to give legal effect to UK withdrawal without an agreement would be legally valid. Both of those assumptions are open to legal challenge.

Creating a second time-limit

Article 50 of the Treaty on European Union creates a two-year time-limit for negotiation of an agreement which, on this occasion, expired on March 29, 2019. Article 50 allows for the extension of the period of negotiation beyond that date. It does not expressly confer a power to create a second time-limit leading to the automatic withdrawal of a member state. It has apparently been assumed that Article 50 confers such a power by necessary implication.

The rules of International Law on treaty interpretation say that if the plain meaning of a treaty text, let alone an implied meaning, leads to a result that is manifestly absurd or unreasonable, another interpretation is possible, giving effect to the object and purpose of the treaty text as a whole.

Withdrawal from the EU under Article 50 is withdrawal byagreement. It does not confer a power of unilateral withdrawal permitted by many other international treaties. So-called no-deal Brexit on October 31, 2019 would amount to allowing the UK, one of the largest EU member states, to withdraw unilaterally by means of its own failure to act, completely regardless of the interests, policies and politics of all the other member states which would be profoundly affected by such unilateral withdrawal, and regardless of the enormous worldwide effects of a unilateral UK withdrawal, including legal chaos in the UK and the EU and in countless other legal systems and situations across the world. To give such a meaning to Article 50 is manifestly absurd and unreasonable.

On this view, the International Court of Justice, the ECJ or the UK Supreme Court (after obtaining a preliminary ruling from the ECJ) could decide that, if the agreement of 10 April 2019 extending the period of negotiation had created a second time-limit leading to an automatic UK withdrawal, then that would have been an unlawful act (lacking a legal basis) and hence invalid (without legal effect).

EU implementation of UK withdrawal

The EU institutions would give legal effect within the EU to the withdrawal of the UK without a withdrawal agreement. Unless the EU’s constitutional treaties were amended between now and October 31, which is not possible, the existing system of decision-making in the EU institutions would apply. The EU has seven primary institutions with decision-making powers. The European Parliament, the European Council, the Council, the European Commission, the ECJ, the European Central Bank, the Court of Auditors.

Leaving the last two institutions on one side for present purposes, each institution has its own decision-making powers, and also powers exercised in conjunction with one or more other institutions. In the case of legislation, such as regulations and directives, the typical process involves joint action by the Commission, the Council and the European Parliament. Typically also, decisions in the Council are made by unanimity or by a qualified majority.

Article 50(4) excludes representatives of the withdrawing member state from participating in the discussions of the European Council or the Council on the negotiation and conclusion of the withdrawal agreement ‘or in decisions concerning it’ (a painfully imprecise phrase). A special form of ‘qualified majority’ is created for this purpose. The text does not preclude the participation of representatives of the withdrawing state in the decision-making of the European Parliament, including legislation implementing UK withdrawal, in which the European Parliament must be involved as a co-legislator.

If Article 50(4) does not exclude the participation of UK members of the European Parliament in decisions implementing UK withdrawal, the UK members of the European Parliament would be entitled to take part in those decisions and, if they were prevented from participating, the decisions would presumably be invalid.

If there is no valid agreement or decision creating a second time-limit, then all decisions of the EU institutions giving effect to UK withdrawal without an agreement, whether made before or after October 31, would be invalid.

The ECJ is frequently called upon to consider the legality and validity of acts of the EU institutions. This classic constitutional and public law jurisdiction can be exercised before or after a decision is made.

Philip Allott is Professor Emeritus of International Public Law at Cambridge University.